Radio transmission system



R. A. HEISING 5,858

RADIO TRANSMISSION SYSTEM Filed April 29, 1924 myeflior: fiaymaMA HHS/byPatented Mar. 19, 1931 innran stares earner QFFICE I nnrivronn A.nnrsrncr; or MILLBURN, new anRsnY, AssreNoR T WESTERN ELECTRIC ooMrAnY,moonrona'rnn, on NEW YORK, N, Y., A conronerron or new YORK 'nenrornensnrssion SYSTEM Application filed. April 29,

This invention relates to radio transmission systems and moreparticularly to modulating systems wherein the generationof' un desiredwave components is substantially prevented. r v

An object of this invention is to produce a completely modulatedwave'and to substantially prevent the generation of undesired componentstherein. e

- Another object is to reduce the energy consumed in a modulating systemwhen no signals are being transmitted thereby.

An additional object is to produce a modulated Wave having'side bandcomponents only which correctly represent the modulating wave. i i Afeature of the invention relates to means for the transmission of radiosignals and for preventing loss of'ene'rgy when no signals aretransmitted. I

=Another feature concerns .the arrange ment wherein complete modulationof high frequency waves is effected without the introduction ofcomponents resulting from distortion and whereby the modulated waves maybe delivered directly to an antenna. A further feature isan" arrangementof space discharge tubes for causing interaction betweencarrier andsignal waves and for suppressing the unmodulated components of carrierfrequency resulting therefrom by shifting the phase of the carrier wavessupplied to the antenna during alternate; half cycles of signal waves. 1

Broadly,'this invention comprises a source of signal waves controllingan arrangement of space-discharge tubes for amplifyingthe signal waves,which arrangement is coupled to a source of high-power high-frequencywaves whereby they are combined with the signal waves directly in aload-circuit such as an antenna or a wire line. The space dischargetubes may be so adjusted as to producecomplete modulation and arepreferably connected in the so-called push-pull arrangement forpreventing the production of undesired components tending-to producedis-v tortion of the signals. The invention also includes facilities forpreventing'the transmission of unmodulated components of carrier 1924.Serial No. 709,737.

frequency and for reducing the energy consumed during the periods whenno signals are being transmitted. As a meansof'effecting carriersuppression the signal waves are arranged to control the source of spacecurrent for a high frequency amplifier in such a manner that duringalternate 'halfcycles of the slgnal waves the phase of carrier waves inthe amplifier circuits is shifted to reduce thelr efiective amplitude toany desired degree or even to Zero. The signal waves also actto stop theflow of space current in the high frequency amplifier so that no highfrequency waves may be transmitted therefrom when no signal waves aresupplied thereto.

To reduce the consumption of energy in the signal amplifier when nosignals are transmitted a negative potential is supplied to the controlelectrodes thereof suflicient to prevent the flow of space current.

In the drawings: Fig. 1 illustrates a radio transmitting system forsupplying high-power completely modulated waves directly to an antennawith-'- cate similar parts.

The modification shown in Fig. 1 comprises a source of signals 10, hereshown as a microphone transmitter, coupled to a pushpull space dischargeamplifier having its output circuit coupled to the output circuit of aspace discharge oscillator by means of an ad ustable auto transformer25.The

oscillator 30 is coupled to an antenna 40. The

source of signals 10 is connected in serieswith a battery 11 and theprimary winding of a transformer 12, the secondary winding-of whichiisdifferentially connected to the baianced input circuits 18 and 14connected re-v spectively to the control electrodes of space dischargetubes 15 and 16. The midpoint of the secondary winding is connected inseries with a grid polarizing battery 17 in common to the cathodes oftubes 15 and 16. circuits 18 and 19 are connected respectively to theanodes of tubes 15 and 16, and include separate portions of the windingof adjustable transformer 25. A common path between a mid tap oftransformer and the cathodes oftubes 15 and 16includes a source of spacecurrent 26, here shownas a battery.

The oscillator includes a space discharge tube 31, and an anode circuitthereof which is connected to an adjustable tap of transformer 25. Theanode circuit may be traced as-follows: anode of tube 31, high frequencychoke coil 32, a portion of the winding of transformer 25,- battery 26to the cathode of tube13'1.

The highfrequencychoke coil 32 is pro vided in thiscircuitin order toprevent high frequency waves from flowing in the space currentcircuit-of the amplifier 20 and the oscillator 30. Battery 26 it is seenserves tosupply space current to all the tubes of the system. Oscillator30 includes in addition an input circuit-connected to the controlelectrodeand-cath-ode oftube 31 which may be traced'trom-this electrodeto coil 33, leak resistance 36 shunted by blocking conoenser to thecathode of tube 31'. The output circuit of-tube' 3'1 is'connectedbetween its cathode and'anode'and includes coil 37 shunted by condenser38" in series with a second condenser 39.

The input and output circuits of oscillator 30- are'associated in energytransfer relation whereby continuous high frequency oscillations-areestablished in the circuit. Antenna 40 is directly associated with theoscillator 3O by thecoupling between coils 37 and 42, 33 and Mrespectively. The antennais connected-to ground in series with acondenser 41' and coils 4-2, l3 and 4e. Coil 43, which is adjustablewithin the coils 4:2 and la, in combination therewith, constitutes avariometerfortuningthe antenna circuit to the frequency of waves to betransmitted. The tuning of the antenna determines the frequency ofoscillations. generated by oscillator 30.

Signalwaves from'source 10 are supplied to the input circuits of tubes15 and 16 through transformer 12. rangement is such that when the wavesfrom source 1O tend to reduce" the negative potential-on the controlelectrode of tube 15 they simultaneously tend to increase the negativepotential'on the controlelectrode of tube 16. Thus,- am'plifiedsignalwaves are repeated in theoutputcircuits of tubes 15 and 16 duringalternate halfcycl'es of the impressed waves from source 10 ina mannerwell understood.

Battery 17 is provided to supply a suitable average potential on thecontrol elec- Output.

The circuit a'rtrodes. This potential may be such that when no signalwaves are supplied to the tube the space current therein is reduced invalue or completely stopped.

Space current is supplied to tubes 15 and 16 by battery 26 connected tothe anodes thereof through respective portions of the winding oftransformer 25. Battery 26 is also arranged to supply space current tothe tube 31'. The anodeof thistube is connected to an adjustable tapon'tra-nsfo'rmer 25. By adjustment of this transformer signal waveshaving the proper degree of amplification to periodically reduce thehigh frequency waves to zero amplitude, that is to produce completemodulation of waves generated byoscillator 30, are supplied to theanodecircuitof tube 31. By virtue of the coupling between the input andoutput ,circuits'oI tube'31 highpower high-frequency waves are generatedin the oscillator. These waves-are combined in the output circuit withsignal wavesfrom amplifier 20 to produce a signalmodulated wave in amanner well understood.-- These modulated waves are supplied directly;to the antenna 40 at coil-l2 and the energy the'reofis raoiated intospace.

Condenser 39 in the output circuit-oftube 31 prevent-stile fiowof spacecurrent in this circuit under the action ofbattery 26., Leak path 35, 36is provided to allow the proper accumulation ofnegative charge on, thecontrol electrode of tube 31.

There is illustrated-in Fig... 2- a radio trans mitting systemcomprising a source of signals 10, coupled to a push-pull amplifier 20which in turn is coupled in tandem to a second push-pull amplifiersupplied with energy from a source of high frequency' waves 60 andcoupled to antenna 70. The amplifier 20' of this figure corresponds tothe amplifier 20 of r Fig- 1 but in this-figure the output circuits 18*and 19: are connected. respectively through the primary winding oftransformer 27 to a source of space current 29, here shown as adirectcurrent generator;

The amplifier 50 comprises spacedischarge tubes- 51" and 52 having theiranode circuits connected in balanced relation to the secondary windingof transformer 27 and inchidingchoke coils 53 and5t; The midpoint of thesecondary winding'of transformer 27 is connected by a common lead'to thecathodes of tubes 51 and 52. The primary winding of transformer 55 issupplied with" highfrequency waves from a source and the secondary ofthis-transformer supplies'these wavestothe ba lanced input circuits oftubes 51 and 52connected between their respective control electrodes andcathodes: The midpoint of the secondary winding is connected through agrid polarizing battery 56 to the cathodesofthe tubes. 7

The amplifier 50' also comprisesbalanced output circuitsc'onnectedrespectively tothe a carrier frequency. The phase of the unmoduanodes oftubes 51 and 52 and including respectively the condensers 57 and 58having their adjacent terminals connected to one terminal of a coil 59,the opposite terminal of which is connected to the cathodes of the tubesthrough switches 28. An antenna is connected to ground in series withcoil 71, which is coupled to coil 59. By operating switches 28 thefilter 61 may be connected in the common branch of the output circuit ofamplifier 50.

Source 10 and amplifier 20 are arranged to supply positive pulsescorresponding to alter nate half cycles of amplified signal waves to therespective anode circuits of tubes 51 and 52 through transformer 27. Noother source of anode potential is provided for the tubes 51 and 52,consequently when no signals are supplied fro-m source 10, no spacecurrent flows in these tubes. Source 60 supplies high frequency Wavesthrough transformer 55 to the inputcircuits of tubes 51 and 52. Hence,when signal waves are supplied to the anode circuits, the high frequencywaves corre-' sponding to those produced by source 60 are repeated inthe anode circuits of the tubes and modulated in amplitude in accordancewith the signal waves. During positive half cycles of signal waves, highfrequency waves are repeated and modulated in the output circuit, of onetube, whereasduring the negative half cycles the high frequency wavesare modulated in the output circuit of the opposite tube. i

The waves produced in the output circuits are supplied through coil 59connected in common thereto whereby the waves from one output circuitare in out of phase relation with Waves of the opposite output circuit.Thus, there appear in the antenna circuit coupled to the coil 59, sideband frequencies without any unmodulated component of the latedcomponent is reversed during each half cycle of the signal wave, thisbeing a characteristic feature of this type of carrier suppressionsystem.

To suppress one side band the filter 61 may be connected by operatingswitches 28, as already described. This filter is designed to have highinput impedance to the undesired side band and low input impedance tothe desired side band. The input impedance referred to is the impedanceoffered by the filter in the path connecting switches 28 when they arethrown to put filter 61 in circuit.

' The transmission band of this filter will be the undesired side band.Energy of the Wave components of the undesired side band is transmittedthrough the filter and dissipated in the resistance 61a.

Choke coils 53 and 54: are provided to prevent the passage ofhighfrequency currents,

through the windings of transformer 27.

Condensers 57 and 58 prevent the flow of the unidirectional or lowfrequency current through the output circuits of tubes 51 and 52. p 1

The potential on the control-electrodes of tubes 15 and 16 may beadjusted by means of battery 17 to a value such that no space desiredside band'is suppressed. The waves 1 within the desired side band aretransmitted by the filter to the transformer 590; and 'impressed uponthe antenna circuit.

The filters Gland 63 are of the well known band-pass type or may be'ofany other type having similar transmission characteristics. Thisinvention has been illustrated in certain specific embodiments but it isintended to be limited only by the scope of the appended claims. v c

-VVhat is claimed is:'

1. In combination, a plurality-of pairs of space discharge amplifiers,one pair having their output circuits electrically coupled-to the outputcircuits of the other pair, means for supplying signal wavesto one pairof said amplifiers, means for supplying high frequency waves to anotherpair of said amplifiers, and means for producing a fiow of space currentin one pair of said amplifiers, only when signal waves are supplied tothe other pair of said amplifiers.

2. In a radiant energy signaling system, a space discharge amplifierhaving input and output circuits, said input circuit being supplied withwaves of high frequency, a source of signals, a push-pull spacedischarge amplifier supplied therewith, said last named amplifier beingcoupled to the output circuit of said first named amplifier, means forcausing a flow of space current in the output circuit of said firstnamed amplifier only during the time when signal waves are supplied tosaid second named amplifier, and means for shifting the phase of wavecomponents of high frequency in the output circuit of said first namedamplifier whereby the unmodulated component of said high frequency wavesis substantially suppressed in said output circuit.

band frequency with no unmodulated' com- 3. In a radiant energysignaling system, 7

ponent of the carrier frequency waves "in the output circuit of saidsecond amplifier, a load circuit connected directly to said outputcircuit, and means included-in said out- I put circuit for suppressingcertain of said Waves of side band frequency.

4. In a radiant energy signaling. system, a source of signal Waves, asource of carrier Waves, a space discharge modulator supplied with saidWaves whereby side bands are produced, an output circuit for saidmodulator traversed by said side bands, and a filter in said outputcircuit, said filter having high impedance to the undesired side band,the transmission band of said filter including said undesired side band.

5. In a radiant energy signaling system, a source of signal Waves, asource of carrier Waves, a space discharge modulator having its inputcircuit connected to said source of carrier Waves and its output circuitconnected to said source of signal Waves, whereby Waves of side bandfrequencies are produced in said output circuit, and a filter in saidoutput circuit having high impedance to an undesired side band, thetransmission band of said filter including an undesired side band saidfilter having a resistance connected across its terminals remote fromsaid output circuit.

In Witness whereof, I hereuntosubscribe my name this 28th day of April,A. D. 1924:.

RAYMOND A. HEISING.

